Rain- induced cross polarization is an important factor in the design of dual-polarization microwave radio communication systems. In this work we present the scattering effect of oblate spheroidal raindrops on Earth-space wave communication in the frequency band 1–52 GHz in three tropical locations: Ile-Ife, Nigeria (4.34⁰E, 7.33⁰N), Douala, Cameroon (9.70⁰E, 4.05⁰N), and Nairobi, Kenya (36.75⁰E, 1.30⁰S). The present study employs the more realistic distribution of canting angles along the path. Results obtained show that the XPD improves by about 4-7dB over those based on the equi-orientation model. Elevation angles of 23⁰ and 55^o are assumed for wave propagation in the regions. The incident waves are assumed to be linearly polarized. The tropical lognormal raindrop size distribution model has been used to estimate the raindrops number density. The specific attenuation and specific phase shift are calculated in terms of the power law relationship between attenuation and rainfall rate since measured cumulative distribution of rain rates are available from the locations. The calculation of the propagation parameters is based on the measured Mean Annual (MA) and Mean Worst Month (MWM) rainfall rates in each location. The predicted copolar attenuation (CPA), and cross-polarization XPD for Cameroon is closer to those obtained for Nigeria than that for Kenya. At the elevation angle of 55⁰, and for links over the Atlantic Ocean Region (AOR), the CPA and XPD are higher in Cameroon than Nigeria by about 24% at the most. At the elevation angle of 23⁰, and for links over the Indian Ocean Region (IOR), the percentage difference between CPA and XPD in Cameroon is higher than in Nigeria by about 1136%. Therefore, it can be safely said that rain induced degradation of Earth-space communication will be most severe in Cameroon and least in Kenya.

Keywords: Cross-polarization discrimination, co-polar attenuation, specific attenuation, specific phase shift

> Nigerian Journal of Physics Vol. 17S 2005: pp. 233-244